Assigning parameters or constraints to a model?
You could add Shape Keys to change the size of things in the object. Also you could try to do it with hook modifiers. Another way to do that thing with the hole you mentioned would be to add a boolean modifier to the main mesh and set it to difference. Then add a Cube (Or whatever the Hole has to be shaped like) and translate it to the correct position. Put the name of the cube in the boolean modifier field and then you can control the hole by scaling that cutout object.

But your task sounds more like a thing to do in scad.